Core drilling apparatus



April 23, 1963 H. HENDERSON CORE DRILLING APPARATUS .unna 0 3 Sheets-Sheet 1 Illl C ra nlu Filed July 27. 1960 Homer l'. Hen ders on IN1/mms.

AT TORN E Y.

April 23, 1963 H. HENDERSON CURE DRILLING APPARATUS 3 Sheets-Sheet 2 Filed July 27, 1960 Hom er Hen demon INVENTOR.

Bmw /2 ATTORNEY.

April 23, 1963 H. l. HENDERSON 3,086,602

CORE DRILLING APPARATUS Filed July 27, 1960 3 Sheets-Sheet 3 Hom er Hen ale/son IN V EN TOR.

BY mana gaw ATTORNEY United States Patent O 3,086,662 CGRE DRILLlNG APPARATUS Homer I. Henderson, San Angelo, Tex., assigner to Strato Drill, lne., San Angelo, Tex., a corporation of Texas Filed July 27, i966, Ser. No. 45,692 9 Claims. (Cl. 17E-404) This invention relates to core drilling apparatus and, more particularly, to a device operated in combination with a core drill for breaking cores into segments of a size range suitable for transportation to the surface under pressure of the circulating drilling iiuid.

This invention is particularly adapted to the type of rotary drill wherein the drilling fluid or mud descends through an annular space, either outside the pipe or between two concentric pipes and ascends within the central core passageway carrying therewith the bit cuttings and severed core segments. In this method of core drilling it is essential that the core be broken into segments of such length as to be suitable for drill fluid transportation to the earths surface. Preferably, of course, the cores must be short enough to be carrie-d to the surface by the available fluid pressure but it is .also desirable that they be long enough to slide upwardly through the core tube without tumbling. However, virtually all oil drilling is conducted through sedimentary formations `having low mechanical strength through horizontal planes. Consequently, precise control of the planes along which cores are severed from the formation is not possible by known methods and inevitably cores will occasionally break off at lengths shorter than desired. When such short core segments twist, turn and tumble upwardly through the core tube to the surface it is difcult to determine the precise arrangement of strata, but such cores nevertheless yield valuable information and do not, therefore, represent too serious a disadvantage. However, serious difficulties do arise when, as it frequently happens cores are short enough to tumble but too long to pass by obstructions in the core tube, particularly the core breaker itself. When this happens, subsequent cores become log jammed behind the lodged core segment until uid circulation is impeded `and/or the drill bit itself becomes inoperative. As a consequence, it is usually inevitable that drilling cornes to a complete standstill.

It is, therefore, one object of this invention to provide a core breaking apparatus designed to break formation cores into suitable lengths to be transported without tumbling to the earths surface.

It is a further object of this invention to provide core breaking apparatus that prevents tumbling of all cores except those short enough to pass freely by core tube obstructions, including the core breaker itself.

It is a further object of this invention to provide core breaking apparatus for a rotary drill utilizing a circulating fluid with a core tube passage adapted to permit maximum flow past a core still attached to the formation and maximum pressure drop across a core after it is severed from the formation.

In carrying out this invention a cam is provided within the central core tube passageway adapted to engage the cores and apply bending moments thereto until the core is severed from the formation. It often happens that cores are severed at shorter lengths than is desired and if such lengths are short enough to tumble, i.e. rotate about a radial axis, they could impinge upon the cam in a crosswise disposition and, if not short enough to pass freely by the cam, may become lodged within the core breaker section. Consequently, an arcuate segment is attached to the core breaker Section of the drill pipe in the crosssectional area below the cam in order to reduce the diametrical distance across the drill pipe enough to prevent 3,086,602 Patented Apr. 23, 1963 ICC tumbling of those cores long enough to lodge in the drill string. As an additional feature of the invention, the diameter of the core breaking section is enlarged to permit free flow of fluid and cuttings past the still attached core but is gradually restricted to provide for greater pressure drop across the length of the core to facilitate transportation thereof to the surface.

Other objects and advantages of this invention will become apparent from the specification following when read in connection with the accompanying drawings where- FIGS. 1 and 2 are vertical section views of a coring type drill incorporating a prior type of core breaker;

FIG. 3 is a vertical section of a core drill incorporating features of this invention;

FIG. 4 is a section taken along line 4 4 of FIG. 3;

FIG. 5 is an isometric view showing the relationship between a core and the core breaker of this invention;

FIGS. 6, 6a and 7 are schematic illustrations showing the effects of tumbling core segments disposed crosswise in the core breaker section;

FIG. 8 is a longitudinal vertical section of the preferred embodiment of this invention; and

FIGS. 9 and 10 are section views taken along lines 9-9 and 10-10 of FIG. 8.

Referring now to the drawings, we have shown a type of core drilling apparatus presently in use comprising an -outer drill pipe 1 to the lower end of which a drill bit 3 is threaded at 4 to cut a bore hole into the earth 8 as the drill pipe 1 is rotated at the surface. A core tube 2 is concentrically spaced within the drill pipe 1 to provide an annular passage 19 for downward flow of drilling fluid in the direction of the flow arrows 7. After owing down between the drill pipe 1 and core tube 2, the drilling fluid passes through the bit nozzle above the bottom of the well into the bore hole annulus 20 and then around the bit 3 into the annular space 16 between the core 10 and the core tube 2 carrying the cuttings 9 and core segments 10o therewith to the earths surface. The core tube 2 is secured against rotation relative to the drill pipe 1 and rotates therewith being spaced therefrom by radial fins 15 welded to the core tube (FIGS. 4, 9 and 10). The lower end of the core 2 is sealed to the bit 3 by a flexible pack ing such as an O-ring 5.

In some previously used core breakers, as illustrated in FIG. l a cam 11 is secured as by welding to the lower end of the core tube 2 and at a measured distance above the lower end of the bit 3. The purpose of the cam is to engage the core 10 as the drill bores deeper into the earth 8 to force the core off center and subject it to a rotating bending moment and in fact, considerable torque because of frictional engagement, It is desirable that the core segments be long enough so that they cannot tumble within the core tube but still not so long as to be excessively heavy or unable to negotiate any and all curves in the core tube 2. As long as all cores break at the maximum length this device works satisfactorily. However, when a core segment 10a is broken at a length short enough to tumble, it may lodge or jam under the cam 11 as shown in FIG. 2. Thereafter, other cores and even cuttings are lodged behind the initially lodged core until a hopeless jam occurs, hindering circulation and often preventing further drilling.

In the present invention illustrated in FIGS. 3, 4 and 5 an arcuate segment l2 of tubing or the like is secured to the inner surface of the core tube 2 as by welding at 14 to extend from just above the bit 3 upward to the core breaking cam 13. The segment 12 is of such thickness as to allow a minimum amount of clearance 17 (FIG. 9) between the segment and the unbroken core 10 to minirnize the possibility of tumbling after severance. If deaccadere sired, the cam may be secured directly to the upper surface of the segment 12 and may be formed of weld material subsequently ground to contour. Occasionally, as above pointed out, cores of shorter length are broken off unavoidably and such cores are shown schematically in FIGS. 6, 6a and 7. In FIG. 6, there is shown a core of normal diameter D and maximum tumbling length L1 (FIG. 6a) presenting a lateral cross-section when tumbling about the Y axis of the core tube 2, it is however sufficiently small to pass freely past the cam 13. In FIG. 7 is shown a second core of maximum length L2 short enough to permit the core while tumbling about the X access to pass by the cam 13. As shown in FIGS. 6 and 7 the edge of cam 13 constitutes a chord of the arcuate segment so that any core segment that passes or bridges the member 12 will pass the cam 13. If desired the arcuate member 12 could extend beyond the cam 13 to further restrict the length L2 of tumbling cores. Of course, the diameter D remains substantially constant for all core lengths 10a and it is the length L that for all practical purposes determines the capacity of the core 10a to pass through the core breaker section. It is not the purpose to stop all core segments from tumbling but to stop from tumbling those core segments that are long enough to jam. In FIG. 6a the function of the segment 12 is shown schematically. Since cores of length L1 will pass freely by the cam 13 while longer cores may be lodged thereagainst, it is desirable to prevent all cores longer than the freely passing core length L1 from tumbling within the core breaker until after it passes by the cam 13. Thus, the arcuate segment 12 is formed of such thickness that the diametrical distance from any point thereon to the opposite Wall of the core tube 2 is no greater than the square root of the sums of the squares of the critical length and the normal diameter. Assuming the critical length is found to be L1, the diametrical clearance below the core breaker 13 should not exceed The cam 13 and the spacer segment 12 must be considered jointly in designing the core breaker section so that the cam 13 is large enough to assert desirable bending moments but not so large that the spacer member 12 has to be formed of a thickness too great to permit the unbroken core to pass.

Referring now to FIGS. 8, 9 and l0, the entire core breaker section is shown and it can be seen that the core tube 2 converges upwardly from a relatively large crosssectional area near the drill bit 3, which permits free passage of the cuttings 9 and full fluid flow past the unsevered core 10, minimizing pressure build-up. At a point spaced above the cam 13 the diameter is reduced to provide a very small clearance around the severed core segment 10a. It is highly desirable that once the core segment 10a is above the core breaker and in the core tube that there be a small cross-sectional area in the annulus 18 between the core segment 10a and the core tube 2 for maximum pressure drop across the' core segment. In practically all cases of drilling, turbulent fluid ow is involved and the equations for determining pressure drop is:

When considering a free core segment 10a, the value of P must be great enough so that when this pressure is multiplied by the cross-sectional area of the core segment the force obtained will exceed the weight of the core when buoyed up by the drilling fluid. Since this amount of force, and hence the corresponding amount of pressure, must always be developed within the core tube in order to get core scavenging, the minimum limit of P is for all practical purposes fixed.

F, the friction `factor is also fixed and L, the length of `the core, is fixed for a given system.

p is the density of the drilling [luid and it is highly desirable to keep this at a minimum for more eflcient drilling.

V is the velocity of the drilling fluid in the annulus; and

M is the hydraulic radius of the section under consideration.

Thus, since P, F, L, and p are for all practical purposes fixed, the only two factors that can be varied are V and M. It is apparent from the above formula that if M is large than V must be proportionately large in order to achieve the necessary pressure drop P. This can be done only by increasing the pumping rate and of course, this causes an increase in pressure in the bore hole annulus which is highly objectionable. On the other hand, if M is decreased the necessary pressure drop can be achieved with a normal pumping rate or even possibly with a reduced pumping rate and this would be highly desirable.

In the preferred embodiment shown in FIG. 8, a special core breaker tube 22 maybe threaded at 23 onto the lower end of the core tube 2. The special tube 22 gradually increases in diameter moving downwardly until it terminates in the cylindrical section 21 which carries the core breaker tube segment 12 and cam 13. With this arrangement, ll achieve the desirable condition of the large annulus 16 (FIG. 9) around the severed core 10a. As shown above this preferred embodiment permits a lower pumping rate with the desirable lower bore hole pressures.

While I have shown a preferred embodiment of this invention, it is apparent that modifications and changes thereto can be made without departing from the spirit and scope of this invention which should `be limited only by the claims appended hereto.

Having described my invention I claim:

l. Core drilling apparatus comprising a tubular drill string adapted to be rotated at the surface of a well while drilling fluid is circulated down to the bottom of said well and then back to the surface through said tubular drill string,

an annular drill bit at the lower end of said drill string adapted to cut into a formation leaving a core of said formation substantially of a predetermined diameter,

a cam member Within said drill string a fixed distance above said drill bit extending inward from one side thereof an amount sufficient to engage said core to impart bending stresses thereto to break said core into core segments, and the internal diameter of said drill string below said cam member being greater than the internal diameter of said drill bit,

means disposed longitudinally within said drill string on said one side thereof between said cam and spaced inwardly from said one side thereof an amount sufficient to reduce diametrical distances to the opposite side of said drill string an amount suicient to prevent tumbling of all core segments too long to pass laterally `by said cam.

2. Core drilling apparatus comprising a tubular drill string adapted `to be rotated at the surface of a well while drilling fluid is circulated down to the bottom of said well and then back to the surface through said tubular drill string,

an annular drill bit at the end of said drill string adapted to cut into a formation leaving a core of said formation substantially of a predetermined diameter,

a cam member within said drill string a fixed distance above said drill bit and extending inward from one side of said drill string adapted to engage and impart bending stresses to said core to break said core into core segments,

the cross-section of said drill string at the level of said cam member being sufficient to permit the passage of all core segments the axes of which are disposed generally lengthwise thereof but being insufficient to permit passage of all core segments longer than a given length the axes of which are disposed generally crosswise thereof, and

means disposed longitudinally within said drill string on said one side thereof between said cam and spaced inwardly from said one side thereof an amount sutcient to reduce diametrical distances to the opposite side of said drill string an amount suicient to prevent tumbling of all core segments longer than said given length.

3. Core drilling apparatus defined in claim 2 wherein said last-named means reduces the diameter of free core passageway within said drill string `below said cam from said one side to the opposite side thereof to a length no greater `than the square root of the sum of the squares of said predetermined diameter and said given lengths.

4. The core drilling apparatus defined in Claim 2 wherein Said drilling tiuid is circulated to flow upward through said tubular tube string to carry said core lengths to the surface of the well, and wherein said drill string is of enlarged diameter from said drill bit `to said cam to permit free circulation of iiuid around cores still attached to the formation and gradually converges to a restricted diameter spaced above said cam to increase pressure drop across the length of severed core segments.

5. Core drilling apparatus comprising a tubular drill string adapted to be rotated at the surface of a well while drilling tiuid is circulated down to the bottom of said well and then back to the surface through said tubular drill string,

an annular drill bit at the lower end of said drill string adapted to cut into a formation leaving a core of said formation substantially of a predetermined diameter, a generally chordal cam member within said drill string a fixed distance above said drill bit extending inward from one side thereof and adapted to engage and impart bending stresses to said core to break said core into core lengths, the cross-section of said drill string at the level of said cam being sufficient to permit the passage of all core lengths disposed generally lengthwise but insufficient to permit passage of core lengths longer than a given length which are disposed generally crosswise, and

an arcuate Segment along said one side of the inner wall of said drill `string extending below said cam shortening the diametrical distances within the are of said segment to the opposite wall of said drill string an amount suiiieient to prevent tumbling of all core lengths longer than said given length.

6. Core drilling apparatus as defined in claim 5 wherein the thickness of said said segment is suflicient to reduce said diametrical distances to a value no greater than the square root of the sum of the squares of said predetermined diameter and said given length.

7. Core driiling apparatus comprising a tubular drill pipe adapted to be rotated at the surface of a well,

an annular drill bit at the lower end of said drill pipe adapted to cut into a formation leaving a core of said formation of a predetermined diameter,

cam member within said drill pipe for breaking said core into core segments,

surface portions spaced inward from said drill pipe below and in the chord of said cam member an amount sufficient to prevent tumbling of core segments too long to pass laterally by said cam member,

the interior of said drili pipe `forming a tiuid passageway for upward ilow of drilling fluid to carry said core segments therewith to the surface of the weli,

the lower end of said drill pipe being of enlarged interna] diameter to permit `free flow of uid past cores attached to the formation and gradually converging into a restricted diameter slightly greater than said predetermined diameter beginning at a level spaced above said core breaking means to provide increased pressure drop across said core lengths.

8. Core drilling apparatus comprising a tubular drill pipe section adapted to be rotated from the surface of the well while circulating drilling fluid is returned from the bottom of said well back to the surface through said tubular drill string;

an annular drill bit at the lower end of said drill pipe section adapted to cut into a formation leaving a core of said formation substantially of a predetermined diameter,

the internal diameter of said pipe section being greater than said predetermined diameter whereby a core of fixed length will span the interior of said pipe section; and

a cam member in the lower portion of said pipe section extending inward from the inner wall thereof an amount sucient to engage said core and impart bending stresses thereto to break said core into core segments,

said cam member being entirely within a chordal segment of the circular cross section of said pipe section defined by a chord equal in length to the longest of said fixed length and said predetermined diameter; and means disposed below said cam member to restrict cores of said tixed length which are disposed with their axes transverse to said pipe to a position wherein said longest dimension is parallel to said chord.

9. The core drilling apparatus defined in claim 8 `wherethe portion of the inner wall of said pipe section below said cam member and within said chordal segment being spaced from the opposite wall a distance no greater than Athe square root of the sum of the squares of said predetermined diameter and said fixed length.

References Cited in the file of this patent UNITED STATES PATENTS 1,644,947 Phipps Oct. 11, 1927 2,514,585 Natland July 11, 1950 2,514,586 Natland et al. July 11, 1950 2,537,605 Sewell ian. 9, 1951 2,540,385 Biggs Peb. 9, 1951 2,634,106 Foster Apr. 7, 1953 2,657,016 Grable Oct. 27, 1953 

1. CORE DRILLING APPARATUS COMPRISING A TUBULAR DRILL STRING ADAPTED TO BE ROTATED AT THE SURFACE OF A WELL WHILE DRILLING FLUID IS CIRCULATED DOWN TO THE BOTTOM OF SAID WELL AND THEN BACK TO THE SURFACE THROUGH SAID TUBULAR DRILL STRING, AN ANNULAR DRILL BIT AT THE LOWER END OF SAID DRILL STRING ADAPTED TO CUT INTO A FORMATION LEAVING A CORE OF SAID FORMATION SUBSTANTIALLY OF A PREDETERMINED DIAMETER, A CAM MEMBER WITHIN SAID DRILL STRING A FIXED DISTANCE ABOVE SAID DRILL BIT EXTENDING INWARD FROM ONE SIDE THEREOF AN AMOUNT SUFFICIENT TO ENGAGE SAID CORE TO IMPART BENDING STRESSES THERETO TO BREAK SAID CORE INTO CORE SEGMENTS, AND THE INTERNAL DIAMETER OF SAID DRILL STRING BELOW SAID CAM MEMBER BEING GREATER THAN THE INTERNAL DIAMETER OF SAID DRILL BIT, MEANS DISPOSED LONGITUDINALLY WITHIN SAID DRILL STRING ON SAID ONE SIDE THEREOF BETWEEN SAID CAM AND SPACED INWARDLY FROM SAID ONE SIDE THEREOF AN AMOUNT SUFFICIENT TO REDUCE DIAMETRICAL DISTANCES TO THE OPPOSITE SIDE OF SAID DRILL STRING AN AMOUNT SUFFICIENT TO PREVENT TUMBLING OF ALL CORE SEGMENTS TOO LONG TO PASS LATERALLY BY SAID CAM. 